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Section 5.3 Energy, Temperature Changes and Changes of State

Section 5.3 Energy, Temperature Changes and Changes of State. In this section: heat transfer: specific heat capacity calculating temperature changes changes of state heating curves. HEAT: What happens to thermal (heat) energy?. Three possibilities: Warms another object

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Section 5.3 Energy, Temperature Changes and Changes of State

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  1. Section 5.3 Energy, Temperature Changes and Changes of State

  2. In this section: • heat transfer: specific heat capacity • calculating temperature changes • changes of state • heating curves

  3. HEAT: What happens to thermal (heat) energy? • Three possibilities: • Warms another object • Causes a change of state • Is used in an endothermic reaction

  4. Heat is added to a substance; how much does its temperature increase?

  5. Specific heat capacity: energy required to raise the temperature of a 1 g sample by 1 oC

  6. Determining specific heat capacity Using the following data, determine the specific heat capacity of silver. q = 150 Jm = 5.0 g AgTfinal = 145.0 °CTinitial = 20.0 °C

  7. Trends in specific heat capacity

  8. Heat and Temperature:Key Equation

  9. Calculating temperature change. Calculate the final temperature reached when 324 J of heat is added to a 24.5-g iron bar initially at 20.0 °C.

  10. What happens to thermal (heat) energy? • When objects of different temperature meet: • Warmer object cools • Cooler object warms • Thermal energy is transferred • qwarmer = -qcooler • specific heat x mass x T = specific heat x mass x T • warmer object cooler object

  11. Heat transfer between substances: Specific heats: Cu = 0.385 J/goC Wood = 1.8 J/goC

  12. Predicting Thermal Equilibrium: Conceptually Easy Example: If we mix 250 g H2O at 95 oC with 50 g H2O at 5 oC, what will the final temperature be?

  13. HEAT: What happens to thermal (heat) energy? • Three possibilities: • Warms another object • Causes a change of state • Is used in an endothermic reaction

  14. Thermal Energy and Phase Changes First: What happens? Heating Curve

  15. Thermal Energy and Phase Changes

  16. Thermal Energy and Phase Changes

  17. But what’s really happening? • Warming: • Molecules move more rapidly • Kinetic Energy increases • Temperature increases • Melting/Boiling: • Molecules do NOT move more rapidly • Temperature remains constant • Intermolecular bonds are broken • Chemical potential energy (enthalpy) increases

  18. Energy and Phase Changes: Quantitative Treatment Melting: Heat of Fusion (DHfus) for Water: 333 J/g Boiling: Heat of Vaporization(DHvap) for Water: 2256 J/g

  19. Total Quantitative Analysis How much energy is required to convert 40.0 g of ice at –30 oC to steam at 125 oC?

  20. Total Quantitative Analysis Convert 40.0 g of ice at –30 oC to steam at 125 oC Warm ice: (Specific heat = 2.06 J/g-oC) Melt ice: Warm water (s.h. = 4.18 J/g-oC)

  21. Total Quantitative Analysis Convert 40.0 g of ice at –30 oC to steam at 125 oC Boil water: Warm steam (s.h. = 1.92 J/g-oC)

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